Carbon impregnated paper and method of making same



y 2, 1963 R. M. WHITMAN 3,096,229

mason IMPREGNATED PAPER AND METHOD OF MAKING SAME Filed Oct. 29, 1959 INVENTOR Robert M. Whitman United States Patent 3,096,229 CARBON IMPREGNATED PAPER AND METHOD OF MAKING SAME Robert M. Whitman, Holland Township, N.J., asslgnor to Riegel Paper Corporation, New York, N.Y., a corporation of Delaware Filed Oct. 29, 1959, Ser. No. 849,562 1 Claim. (Cl. 162-435) The present invention relates to the making of carbon impregnated papers, and more particularly to improvements in the making of carbon impregnated photographic papers. In this respect, the invention is not necessarily limited to photographic papers, but has particular applicability in connection therewith.

Papers coated or impregnated with carbon are well known, generally, and are used for a variety of purposes. One of the common uses of such papers is in the photographic field, where the paper is useful in making interleaving sheets or tab stock, for example, or, when coated or impregnated on one side only, as simulated duplex sheets.

Heretofore, the manufacture of carbon impregnated or coated papers has presented certain manufacturing problems, particularly in relation to the handling of the carbon. Thus, one of the conventional manufacturing processes involves the introduction of carbon, usually in the form of carbon black, into the pulp furnish at a preliminary stage of the paper making operation. This has certain disadvantages, particularly in relation to the unavoidable introduction of carbon into the white water system. Moreover, where carbon is introduced in substantial amounts at a preliminary stage, it may interfere with the proper bonding of the fibers during web formation, resulting in a weak web which is diflicult to handle. Another conventional procedure for manufacturing the paper involves first forming the base web material in the usual manner and coating the web at a subsequent time with a carbon-rich coating material. The coating may be carried out in a variety of more or less conventional ways, using roll blade coaters or air knives, for example, or by spraying, dipping, etc. Such procedures usually provide very satisfactory, high-quality coatings. However, they require substantial outlays for the necessary equipment and, in most if not all cases, extra handling is involved, since the coating is not or cannot be carried out as part of the paper making procedure.

In accordance with the present invention, all or most of the carbon is introduced as a part of the paper making procedure, but after the formation of the web. In some cases, part of the carbon may be introduced into the pulp furnish, prior to web furnish, but the amounts of such carbon are maintained sufiiciently low that the problems before described are substantially avoided. More specifically, the process of the invention, in one of its most important aspects, is characterized by the application of carbon to the paper web in a size press or size tub, as a part of the continuous paper making operation. In this way most economical manufacture is realized, without many of the problems inherent in known methods.

In its basic form, the method of the invention comprises forming a web of base stock, as on a conventional Fourdrinier machine, drying or partially drying the web, passing the web through a size press or size tub to coat one or both sides of the web with a carbon suspension, and drying the coated material. Where desirable or expedient, the carbon coated stock may be calendered and/or super-calendered after drying, but such additional operations frequently are unnecessary.

For a better understanding of the invention, reference 3,096,229 Patented July 2, 1963 ice should be made to the following detailed description and to the accompanying drawing, which is a simplified, schematic, flow-sheet representation of the new method.

In accordance with the new method, a furnish is prepared in the usual manner in a heater 10. The furnish may be conventional, but for photographic papers should be so constituted as to be inert to the chemicals normally used in photo-sensitive materials.

The furnish is delivered to a headbox 11, where white water is added in amounts sufi-icient to dilute the stock to a consistency of, for example, solids. The diluted stock is then flowed onto the screen 12 of a Fourdrinier machine 13, where most of the water is drained and returned to the white water system. The wet web of felted fibers formed on the Fourdrinier is transferred to a dryer section 14 where all or most of the moisture remaining in the web is driven off.

After an initial drying in the dryer section 14 the web is passed through a conventional size press 15 or a size tub.

Advantageously, the size press is charged with carbon black material in a liquid form suitable for application to the web as it passes through the nip. A satisfactory form of carbon black is a colloidal dispersion, diluted to about 2% to 6% solids. Usually the starting material is a commercial preparation, such as Aquablak l5, manufactured by Colombian Carbon Company, which is a 30% colloidal dispersion of carbon black. Suiticient additional water is added to the commercial material to achieve the desired, final dilution. It is ad vantageous to incorporate a binder into the carbon black suspension, and conventional starch or casein binders are satisfactory for this purpose. A typical commercial product for this purpose is known as Clearsol gum, which is an oxidized starch manufactured by Penick and Ford, Ltd. The binder may be incorporated in the suspension in amounts approximating 6%.

Advantageously, the several variable relationships at the size press are so adjusted that carbon black is applied to photographic paper stock in amounts ranging between 2% and 10% of the weight of the stock, while the binder constitutes from about 1% to about 6% of the weight of the stock. However, it will be understood that specific intended end uses may dictate that other ranges be used.

After passing through the size press, the carbon coated web is directed into a second dryer section 16, in which moisture of the carbon suspension is driven off. The web may then be calendered and/or supercalendered, if necessary or desirable, in conventional machines 17, 18, and then wound into rolls for eventual use.

For some end uses, such as filmpack tab stock, it is advantageous to incorporate a slip agent into the carbon suspension. A wax emulsion, or a material such as Aquapel 380 manufactured by the Hercules Powder Company, is suitable for this purpose.

The new method has several substantial advantages over methods presently known, particularly in relation to operating economies realized. The application of carbon at the size press, in the manner described, re quires less carbon, as there are practically no losses. Likewise, mill clean-up is greatly simplified, resulting in less machine downtime, and stream pollution, otherwise resulting from the discharge of carbon-laden white water, is eliminated. Special advantages are realized in the manufacture of duplex sheets since, using the new method, lighter weight papers may be used and the manufacture may be carried out on a conventional Fourdrinier machine, rather than on a duplex machine. Duplex type black papers may be manufactured by the new method by making a conventional white or colored paper on the paper machine and treating it on only one side at the size press with a carbon black containing material which will render one side of the sheet black and somewhat conductive.

Another advantage of this process is that papers made by it will be relatively free of pinholes as opposed to those papers made from stock which has carbon black added in the wet form. Carbon black tends to flocculate the fibers making small holes in the matted web which permit light to pass through the sheet.

It should be understood, however, that the specific examples given herein are not intended to be limiting, and reference should be made to the appended claims in determining the full scope of the invention.

This application is a continuation in part of my copending application Ser. No. 716,142, filed February 19, 1958, now US. Patent No. 3,012,928.

I claim:

The method of making photographic papers and the like, which comprises the steps of (a) forming a wet web of fibers which are inert t0 photosensitive materials,

(b) reducing substantially the moisture content of said web,

(c) impregnating said web with a colloidal suspension of carbon black and binder, whose dried residue forms an integral, opaque, pin-hole free impregnation which is inert to photosensitive materials, by subjecting said web to sufiicient rolling pressure in the nip of a size press while said suspension is in contact with at least one surface of the web to bond mechanically the carbon to said Web, and

(d) drying the thus impregnated film.

References Cited in the file of this patent UNITED STATES PATENTS 

